The present invention relates to continuous high-speed band marking of insulated electrical conductors.
Communication and control cables are usually comprised of several or even many individual conductors. These conductors must be identified in some fashion and color-coding is a conventional technique which has been used with advantage for many years. In a typical example, a communication cable uses a number of conductor quads of which three conductors must be provided with different markings, while the fourth one may remain unmarked. The three conductors may be marked, for example, with different color bands placed regularly along the cable. Alternatively, groups of such bands are used to mark the cables, whereby the number of bands per group differs as a distinguishing marking feature. The band groups are likewise spaced regularly along and on the insulation. In a typical case, the spacing from band to band or from band group to band group may be a few centimeters or about one inch.
Several years ago a technique of band marking was developed and became known under the trademark "Colomat". This technique uses ink or dye jets which are directed towards the conductor but undergo periodic deflections so that a jet strikes the passing conductor only very briefly and inscribes thereby a half-band. As the ink-jet deflects up or down, it misses the cable and a length thereof passes by (still) unmarked. The next half-band is applied when the jet returns, and so forth. The jet oscillates, of course, in a plane extending transversely to the direction of the passing conductor. A similar oscillating ink or dye-jet is applied and directed towards the cable along the other side and operates in strict synchronism with the first one to provide the other half of a complete band in each instance. A marking system of this type is, for example, disclosed in British Pat. No. 950,571; (see Austrian Pat. No. 240,450) German Pat. No. 1,465,660, (see also British Pat. No. 1,034,146) and in a paper by G. Lehnert and J. V. McBride, "High speed Band Marking of Insulated Conductors", published in "Wire and Wire Products", April 1964.
This particular "Colomat" has been used with great success. Moreover, it was found to be of advantage to mark conductors in that fashion while the insulation is still hot and passes through a cooling zone, following, for example, extrusion of the insulation jacket onto the metal conductor. Ink and insulation dries together so as to ensure positive adhesion of the marking bands.
In recent years, however, the production line speed of conductors and cable has so greatly increased that the existing equipment for band marking just could not be operated at a commensurately higher speed. It was found, in particular that the jet tends to break up into droplets just about or even before striking the insulation, and the resulting half-band has rather poorly developed and fuzzy boundaries.